Modified freeform fabricated part and a method for modifying the properties of a freeform fabricated part

ABSTRACT

The present invention is a process for modifying the properties of a porous freeform fabricated part by increasing its density and reducing its porosity. The porosity and density of a freeform fabricated part are altered by packing the pores in a freeform part with an infiltrant, such as a preceramic polymer. The process includes drawing a vacuum on or pressurizing the freeform part while it is in an infiltrant bath, thereby forcing the infiltrant into the pores of the freeform part. After removing the densified freeform part from the infiltrant bath, the freeform part is subjected to a treating process, such that the infiltrant within the pores transforms to a ceramic or ceramic-containing phase to thereby increasing the density of the freeform part.

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This is a continuation of U.S. patent application Ser. No.09/847,136, filed May 2, 2001, which is a divisional of U.S. patentapplication Ser. No. 09/311,771, filed May 13, 1999 now U.S. Pat. No.6,228,437, issued on May 8, 2001, which is a continuation-in-part (CIP)of U.S. patent application Ser. No. 09/220,922, filed Dec. 24, 1998, theentirety of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] This invention relates to freeform fabricated parts and inparticular, to a method for modifying the properties of a freeformfabricated part by increasing its density.

BACKGROUND ART

[0003] As a result of the demand for ways to improve manufacturingefficiency and the need for rapid prototype development, freeformfabrication has become a popular method for manufacturing parts.Freeform fabrication originated with a process called stereolithographywherein a focussed ultra-violet laser scans the top of a bath of aphotopolymerizable liquid polymer plastic material, thereby causing thetop of the bath and the area just below the surface to polymerize. Thepolymerized layer is thereafter lowered into the bath and the laserscanning process is repeated until a second polymerized layer is formed.As the second polymerized layer forms, it bonds to the first layer. Thisprocess is repeated until a plurality of superimposed layers form thedesired part. The shape of the part is first designed in a computeraided design system (i.e., a CAD/CAM system), which is linked to themachine performing the stereolithography process. Most freeformfabrication processes include a computer aided design system forcoordinating the execution of the freeform fabrication process. In thecase of stereolithography, the laser beam scans the area of the bathnecessary to form the freeform fabricated part (hereinafter referred toas “freeform part”) designed on the computer aided design system.

[0004] The ability to produce an actual part directly from a designprovides many advantages. One advantage includes eliminating the timetraditionally used to develop the necessary tooling to manufacture thefreeform part. Another advantage includes reducing the amount ofmachining, such as grinding, milling, drilling, etc., required tocomplete the part because the freeform fabrication process produces asubstantially readily usable final product. Minimizing the amount ofhands-on machining, therefore, translates into reducing the amount ofpotential human error and increasing efficiency. The amount of timesaved in preparing for manufacturing also makes the freeform fabricationprocess attractive for rapid prototype development, which has been oneof the main interests surrounding this technology in recent years. Thebenefit of rapid prototyping includes the ability to manufacture variousconfigurations in a short amount of time, thereby providing designerswith actual models of their designs.

[0005] Another method of freeform fabrication includes a techniquecalled Three-Dimensional Printing (3DP), which consists of depositing apowdered material (e.g., a powdered ceramic, powdered metal, powderedplastic, or combination thereof) in sequential layers, one on top of theother. After depositing each layer of powdered material, a liquid binderis selectively supplied to the layer of powdered material using a typeof ink-jet printing technique in accordance with a computer model of thethree-dimensional part being fabricated. Following the sequentialapplication and binding all of the required powder layers, the unboundpowder is removed, thereby resulting in the formation of the designedthree-dimensional part.

[0006] A third method of freeform fabrication includes Selective LaserSintering (SLS). SLS includes a process whereby a powder dispenserdeposits a layer of powdered material into a target area. A lasercontrol mechanism, which typically includes a computer that houses thedesign, modulates and moves the laser beam to selectively sinter a layerof powder dispensed in the target area. Specifically, the controlmechanism operates to selectively sinter only the powder disposed withinthe defined boundaries of the design. The control mechanism operates thelaser to selectively sinter sequential layers of powder, producing acompleted part comprising a plurality of layers sintered togetheryielding the completed design.

[0007] A fourth method of freeform fabrication includes BallisticParticle Manufacturing (BPM). BPM uses an ink-jet printing apparatuswherein an ink-jet stream of liquid polymer or polymer compositematerial is used to create three-dimensional objects under computercontrol, similar to the way an ink-jet printer produces two-dimensionalgraphic printing. The device is formed by printing successivecross-sections, one layer after another, to a target using a coldwelding or rapid solidification technique, which causes bonding betweenthe particles and the successive layers.

[0008] An additional freeform fabrication technique, includes FusedDeposition Modeling (FDM). FDM consists of building solid objects in alayering fashion from polymer/wax compositions by following the signalsproduced by a computer aided design system. Specifically, FDM buildsstructures by extruding a fine filament of plastically deformablematerial through a small nozzle. The computer aided design systemappropriately directs the nozzle over a build surface in the x, y and zdirections, thereby creating a three-dimensional object that resemblesthe design.

[0009] Another method of freeform fabrication includes a techniquecalled Photochemical Machining, which uses intersecting laser beams toselectively harden or soften a polymer plastic block. The underlyingmechanism used is the photochemical cross-linking or degradation of thematerial. U.S. Pat. No. 5,490,962 provides a detailed summary of each ofthe above mentioned freeform fabrication techniques and is herebyincorporated by reference.

[0010] The specific processes described above as being suitable forforming products of the present invention are inherently free of fiberreinforcement. In the main, these processes result in the manufacture orproduction of a freeform based on particulate material. As distinct fromthe prior art directed to making preforms, articles made by the presentinvention do not use fiber reinforcement and therefore are fiber free.

[0011] The methods described above, however, often result in thefabrication of a porous freeform part, thereby creating undesirablemechanical properties for the freeform part. A freeform part havinginadequate strength, unsatisfactory hardness, low temperature tolerance,low abrasion resistance, rough surface finish, poor bonding ofindividual layers or poor bonding of powder particles within the layerspresents a significant limitation to the types of applications in whichfreeform parts can be utilized. Therefore, what is needed is a means forincreasing the mechanical, thermal or other physical properties offreeform parts.

DISCLOSURE OF INVENTION

[0012] The present invention exploits the porosity of a freeformfabricated part by packing the pores of a freeform part with aninfiltrant that is capable of transforming to a ceramic or aceramic-containing phase. The infiltrant comprises a preceramic polymer,which is selected to bond with the freeform part such that the resultingcomposition improves the mechanical, thermal and other characteristicsof the freeform part. Packing the pores of the freeform part, therefore,increases its density and concomitantly decreases its porosity.Particularly, increasing the density of the freeform part increases oneor more or all of the following properties: mechanical strength,hardness, temperature resistance, abrasion resistance, thermalconductivity, and erosion resistance. These properties may be enhancedby carefully fabricating the freeform part such that a certain porosityis imparted, selecting particular infiltrants with variousconcentrations that add the desired properties to the freeform part, andrepeating the infiltration process until the desired density isachieved.

[0013] Accordingly, one aspect of the present invention is a process formodifying the properties of a porous freeform part comprising the stepsof depositing a porous freeform part in an infiltrant bath, drawing avacuum on the porous freeform part and the infiltrant bath such that theinfiltrant enters the pores within the freeform part, and removing thedensified freeform part from the infiltrant bath. The infiltrant isnormally a preceramic polymer that is capable of transforming to aceramic or a ceramic-containing phase. Furthermore, the preceramicpolymer is preferably a polymer capable of nanocrystalline ceramic phasegrowth such that the preceramic polymer can enter the pores within thefreeform part. Upon being removed from the infiltrant bath the densityof the freeform part increases because the previously empty pores nowcontain infiltrant, and the infiltrant within the pores of the freeformpart transforms to a ceramic or a ceramic-containing phase. Subjectingthe freeform part to multiple infiltration processes further decreasesthe porosity of the freeform part and concomitantly increases itsdensity.

[0014] A second embodiment of the present invention includespressurizing the infiltrant as an alternative to or in conjunction withdrawing a vacuum on the porous freeform part and the infiltrant bathsuch that the infiltrant enters the pores within the freeform part.

[0015] A third embodiment of the present invention includes heating theinfiltrant while pressure is being applied.

[0016] A fourth embodiment of the present invention includes placing theporous freeform part in a vacuum dessicator, applying a vacuum andallowing an infiltrant to enter the vacuum dessicator such that theinfiltrant enters the pores within the freeform part.

[0017] A fifth embodiment of the present invention includes subjectingthe densified freeform part to a series of post-processing steps uponbeing removed from the infiltrant bath such that the infiltrant withinthe pores of the densified freeform part transforms to a ceramic or aceramic-containing phase. The post-processing steps may include one ormore or all of the following steps: curing the infiltrant, heating theinfiltrant at a rate, duration and temperature such that the infiltranttransforms to a ceramic or ceramic-containing phase within the pores ofthe freeform article, annealing the transformed infiltrant and coolingthe freeform fabricated part and the transformed infiltrant.

[0018] A still further embodiment of the present invention includes afreeform fabricated part having pores therein comprising a ceramic or aceramic-containing phase disposed within a portion of the pores with thefreeform part.

[0019] The foregoing features and advantages of the present inventionwill become more apparent in light of the following detailed descriptionof exemplary embodiments thereof as illustrated in the accompanyingdrawings.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] Through conducting a series of experiments, the inventor of thepresent invention recognized that infiltrants such as preceramicpolymers, which are inorganic or organic polymers that transform toceramic when subjected to intense heat, are capable of infiltrating thepores of a freeform part. The inventor of the present invention alsorecognized that increasing the density of the freeform part with certaininfiltrants improved the mechanical characteristics of the freeformpart, which serves as a support structure for the infiltrants.Therefore, the present invention is a process comprising the steps offabricating a freeform part, depositing the freeform part in aninfiltrant bath, drawing a vacuum on the porous freeform part and theinfiltrant bath such that the infiltrant enters the pores of thefreeform, and subjecting the freeform part and infiltrant to a treatingprocess that may include one or more post-processing steps. Freeformparts for use in practicing the method of the present invention werefabricated using a three-dimensional printing technique similar to thatdescribed in U.S. Pat. Nos. 5,204,055 and 5,340,656 and 5,387,380, whichare hereby incorporated by reference. Although the freeform parts inthese experiments were made using the three-dimensional printingtechnique, the present invention may be used with freeform parts made byvirtually any known freeform fabrication technique such asstereolithography, selective laser sintering, fused deposition modeling,ballistic particle manufacturing, and photochemical machining. It ispreferable that the freeform parts be capable of withstanding the typeof post-processing steps associated with transforming an infiltrant to aceramic or ceramic-containing phase. Three different types of freeformparts were fabricated using the three-dimensional printing technique.One was a ¼ inch by ¼ inch by 4 inch Acrysol bonded silicon carbide(SiC) part. Specifically, silicon carbide powder, manufactured byWashington Mills under the tradename SIKA I, was bonded by the organicbinder Acrysol WS-24, which is an acrylic colloidal dispersionmanufactured by Rohm & Haas. The second type of freeform part was a ¼inch by ¼ inch by 1 ½ inch alumina part. In that instance, brownaluminum oxide (Al₂O₃) powder manufactured by Norton Company under theproduct code 7131 was bonded by the same Arysol WS-24 binder. The thirdtype of freeform part was also a ¼ inch by ¼ inch by 1 ½ inch aluminapart fabricated using the same brown aluminum oxide (Al₂O₃) powdermanufactured by Norton Company mentioned above using thethree-dimensional printing technique. However, this third type offreeform part was fabricated using the inorganic binder, colloidalsilica (SiO₂), manufactured by the Norton Company under the tradenameNyacol. Although the three freeform-fabricated parts used in ourexperiments were manufactured using silicon carbide and aluminum oxide,other materials such as metal, ceramic and metal-ceramic compositescould be manufactured using the three-dimensional printing technique.Additionally, organic and inorganic binders other than Arysol WS-24 andcolloidal silica could be used in the three-dimensional printingprocess.

[0021] The original density of the three types of parts was about thirtypercent (30%) to about thirty seven percent (37%). In other words, sixtythree percent (63%) to about seventy percent (70%) of thethree-dimensional fabricated freeform part was porous. Therefore, it mayalso be preferable to subject the freeform part to post-processingmethods, such as mild sintering or annealing, but doing so only improvesthe density to about thirty eight percent (38%) to about thirty-nine(39%). In the method of the present invention, the density of a freeformpart is increased by depositing the freeform part into an infiltrantbath consisting of a preceramic polymer (i.e., ceramic precursor), whichcan be an organic or inorganic polymer but is generally in the form ofan inorganic polymer. Any preceramic polymer capable of transforming toa ceramic or a ceramic-containing phase having nanocrystallinestructures therein may be used as an infiltrant. Although the preceramicpolymers used in all of the following examples were in the form of aliquid or a sol-gel, the preceramic polymer could be in a number ofother forms, such as an organic solvent based solution or a liquiddispersion containing solid particles. In the latter case, the liquidprovides a medium to deliver particles into the pores of a fabricatedfreeform part. TABLE 1 Variable No. 1 No. 2 No. 3 No. 4 No. 5 No. 6Infiltrant Alumina Black-glas ™ poly(methyl Perhydrido TyrannoPolyalumino- sol-gel silicon vinylsilane) polysilazane Coat ™ silazaneoxycarbide (PMVS) (PHPS) Polysilazane (PAS) Vacuum Pressure 5 × 10⁻³torr 5 × 10⁻³ torr 5 × 10⁻³ torr 5 × 10⁻³ torr 5 × 10⁻³ torr 5 × 10⁻³torr Vacuum Time 5 to 60 min 5 to 60 min 5 to 60 min 5 to 60 min 5 to 60min 5 to 60 min Composition of Air or Nitrogen or Argon Air, NitrogenNitrogen or Nitrogen Curing Atmosphere oxygen argon or argon argonCuring Temperature 100° C. 85° C. 150 to 250° C. 100° C. 110° C. 80 to200° C. Curing Time 2 hours 5 to 12 hours 1 to 3 hours 1 to 3 hours 1 to3 hours 1 to 3 hours Composition of Con- Air or Nitrogen or Argon Air orNitrogen Nitrogen or Nitrogen verting Atmosphere oxygen argon or argonargon Initial Converting 110° C. 100° C. 250° C. 150° C. 150° C. 150° C.Temperature Rate of Increasing 2 to 10 2 to 10 2 to 10 2 to 10 2 to 10 2to 10 Converting Temperature ° C./min ° C./min ° C./min ° C./min °C./min ° C./min Final Converting 1000° C. 1000° C. 1000° C. 1000° C.1000° C. 1000° C. Temperature Composition of Air or Nitrogen or ArgonAir, Nitrogen Nitrogen or Nitrogen Annealing Atmosphere oxygen argon orargon argon Annealing 1000 to 1000 to 1000 to 1000 to 1000 to 1000 toTemperature 1600° C. 1600° C. 1800° C. 1800° C. 1800° C. 1800° C.Annealing Time 1 to 8 hours 1 to 8 hours 1 to 8 hours 1 to 8 hours 1 to8 hours 1 to 8 hours Rate of Cooling 10° C./min 10° C./min 10° C./min10° C./min 10° C./min 10° C./min

[0022] Referring to Table 1, the freeform parts were deposited in thefollowing preceramic polymers: alumina sol-gel, siliconoxycarbide(SiOC), poly(methylvinylsilane) (PMVS), perhydridopolysilazane(PHPS), polysilazane, and poly(aluminosilazane). Other potentialpreceramic polymers that could be used as infiltrants includepolysilane, polycarbosilazane, poly(borosilazane), polysiloxane andpolycarbosilane, and other molecularly mixed polymers that are capableof producing nanocrystalline ceramics or metals or mixtures hereof.Various polysilanes, polysilazanes, silicon oxycarbide (SiOC),polycarbosilazane, polysiloxane, perhydridopolysilazane andpolycarbosilanes are commercially available. The alumina sol-gel used inExample 1 was prepared using a known process. The silicon oxycarbide(SiOC) used in Example 2 is produced by Allied Signal under thetradename Blackglas. The Blackglasä silicon oxycarbide (SiOC) actuallyconsists of a monomer solution, Blackglasä 489A, and a catalyst,Blackglasä 489C, which are combined before the freeform-fabricated partis deposited into such a bath. The perhydridopolysilazane used inExample 4 is sold by Tonen, and the polysilazane used in Examples 5 isdistributed by UBE under the tradename Tyranno Coat. Although apoly(methylvinylsilane), a poly(aluminosilazane) or a poly(borosilazane)may not be manufactured on a commercial scale, it is known how tomanufacture such preceramic polymers. Particularly, when using apoly(methylvinylsilane), it is preferred to use a reactive endblockedpoly(methylvinylsilane) as described in a Final Technical Reportentitled Novel Precursor Approaches for CMC Derived by Polymer Pyrolysisdated Feb. 15, 1994 prepared under Government Contract No.F49620-91-C-0017 and/or a Final Technical Report entitled A Study of theCritical Factors Controlling the Synthesis of Ceramic Matrix Compositesfrom Preceramic Polymers prepared under Government Contract No.F49620-87-C-0093, which are both hereby incorporated by reference. Also,when using a poly(aluminosilazane) as a preceramic polymer, it ispreferred to produce such poly(aluminosilazane) using the method asdescribed in a Final Technical Report entitled Silicon-BasedNanostructural Ceramics Derived from Polymer Precursors: Development ofProcessing, Structure & Property Relationships prepared under GovernmentContract No. F49620-95-C-0020 and/or in an article entitled Aluminum-27and Silicon-29 Solid State Nuclear Magnetic Resonance Study of SiliconCarbide/Aluminum Nitride Systems: Effect of Silicon/Aluminum Ratio andPyrolysis Temperature in Chemistry of Materials (1998), which are bothhereby incorporated by reference.

[0023] Continuing to refer to Table 1, individual freeform parts weredeposited into a vacuum dessicator that contained each infiltrant.Although each infiltrant, other than the Tyranno Coatä polysilazane, wasnot a solution, it is possible to add a solvent to each infiltrant,thereby decreasing its concentration. Reducing the viscosity of theinfiltrant in order to increase pore penetration by the infiltrant inthe freeform part may be a viable reason for using a solvent to form asolution. After being deposited in the infiltrant bath, a vacuum isdrawn on the freeform parts ranging from about 100 (torr) to about5×10⁻³ (torr). In these experiments, each freeform part and infiltrantwere vacuum pressurized at a pressure of about 5×10⁻³ (torr) for aboutfive minutes to about sixty minutes. The time required to infiltrate thefirst freeform part with the infiltrant varied with each infiltrantbecause of the varying infiltrant viscosity and pore size. Upon packing(e.g., filling) at least a portion of the pores in the first freeformparts with the infiltrant, the freeform part, packed with infiltrant,was removed from the vacuum dessicator and cured, which increased theviscosity of the infiltrant such that the freeform parts retained theinfiltrant within its pores. In these examples, all infiltrants werethermally cured, which is one method of radiation curing. Otherradiation curing techniques include x-ray, microwave, visible orultraviolet light, and electron beam radiation. Depending upon thecomposition of the infiltrant, it is also possible to chemically curethe infiltrant. For example, the Blackglasä silicon oxycarbide (SiOC)may cure by a chemical curing process without any external heat, due tothe combination between the Blackglasä 489A and the Blackglasä 489C.Applying heat to the Blackglasä silicon oxycarbide (SiOC), however,reduces the curing time. Therefore, it is preferred to heat theBlackglasä silicon oxycarbide (SiOC) to a temperature of about 85° C.for about five to sixty minutes according to the manufacturer'srecommendation. As mentioned above, the infiltrant can also include asolvent, but if so, the solvent must be removed from the infiltrant andfreeform part prior to or during the curing stage.

[0024] After curing the infiltrant, the freeform part was placed in anO-ring sealed, fused silica tube (hereinafter referred to as “tube”),which controlled the temperature, atmosphere and pressure used inperforming the converting stage. The tube was only capable ofwithstanding a temperature of about 1000 degrees Celsius. Therefore, thefreeform part was transferred to a ceramic tube, such as an alumina ormullite tube before elevating the temperatures above about 1000 degreesCelsius. Depending upon the infiltrant's sensitivity to air, thecomposition of the atmosphere may include argon or nitrogen in order tomaximize the transformation of the infiltrant to the desired ceramic orceramic-containing phase. The converting stage comprises applying heatto the infiltrant and freeform part such that the infiltrant transformsto a ceramic or a ceramic-containing phase and bonds to the freeformpart. Although it is preferred to increase the temperature of theatmosphere within the tube at a rate of about two degrees Celsius perminute (2° C./min) until the temperature of the atmosphere attains aboutone-thousand degrees Celsius (1000° C.), it is possible to perform theconverting stage by raising the temperature at a faster rate ranging upto about ten degrees Celsius per minute (10° C./min).

[0025] In all instances, the freeform parts were also annealed bykeeping the parts within the tube after the converting stage wascomplete and holding the temperature of the tube constant within a rangeof about one-thousand degrees Celsius (1000° C.) to about one-thousandeight hundred degrees Celsius (1800° C.) for about one hour to abouteight hours. Annealing the infiltrant increases its crystalinity andinitiates additional ceramic grain formation such that the density ofthe freeform part further increases. Finally, the freeform parts werecooled at a preferred rate of about ten degrees Celsius per minute (110°C./min) until the freeform part attained ambient conditions. It is alsopossible to cool the freeform part at a rate ranging from about twodegrees Celsius per minute (2° C./min) to about ten degrees Celsius perminute (10° C./min).

[0026] Referring to Table 2, the resulting composition varied dependingupon the material of the freeform part and the infiltrant. TABLE 2Coupon Part Resulting Material Infiltrant Composition Al₂O₃ Aluminasol-gel Al₂O₃/Al₂O₃ Al₂O₃ Blackglas ™ SiOC/Al₂O₃ Silicon oxycarbideAl₂O₃ poly(methylvinyl-silane) SiC(+C)/Al₂O₃ (PMVS) Al₂O₃Perhydridopolysilazane SiO₂ (with air)/ (PHPS) Si₃N₄(+Si)/Al₂O₃ Al₂O₃UBE Si₃N₄(+Si)/Al₂O₃ Tyranno Coat ™ Polysilazane Al₂O₃Polyaluminosilazane SiC/AlN/Si₃N₄/Al₂O₃ (PAS) SiC Alumina sol-gelAl₂O₃/SiC SiC Blackglas ™ SiOC/SiC Silicon oxycarbide SiCPoly(methylvinyl-silane) SiC(+C)/SiC (PMVS) SiC PerhydridopolysilazaneSiO₂ (with air)/ (PHPS) Si₃N₄(+Si)/SiC SiC UBE Tyranno Coat ™Si₃N₄(+Si)/SiC Polysilazane SiC Polyaluminosilazane SiC/AlN/Si₃N₄/SiC(PAS)

[0027] Although certain infiltrants may have destroyed a portion of theinter-particle bonds formed during the three dimensional printingprocess, such as dissolution of the bond between an organic based binderand the three-dimensional printed part, the density of the resultingcomposition surpassed the density of the original freeform part.Specifically, upon undergoing the infiltration process described hereinand infiltrating the freeform part with Blackglasä silicon oxycarbide(SiOC), poly(methylvinylsilane) (PMVS) Perhydridopolysilazane (PHPS),Tyranno Coat T™ Polysilazane, and Polyaluminosilazane (PAS), the densityof the freeform part increased to about fifty percent (50%) to aboutsixty percent (60%). The density of the freeform part infiltrated withthe alumina sol-gel increased to about forty percent (40%) to aboutforty-five (45%).

[0028] The infiltration process of the present invention, therefore,decreased the porosity and increased the density of the freeform part.The density of each freeform part is further increased and its porosityfurther decreased upon repeating the process until the desired densityand porosity are achieved. It is beneficial to practicing the process ofthe present invention to first engineer the porosity of the freeformpart to receive the infiltrants. Specifically, by fabricating freeformarticles having an adaptable porosity, varying the type of infiltrant,controlling the concentration of the infiltrant and subjecting thefreeform part to various and multiple infiltration processes, one canmanipulate the porosity and mechanical characteristics of a freeformarticle such that a freeform part having desired properties of hardness,strength and density is produced.

[0029] An alternate process for modifying the properties of a porousfreeform-fabricated part comprises the further step of pressurizing theinfiltrant after drawing a vacuum on infiltrant and freeform part. Thispressurizing step increases the potential of packing the pores in thefreeform part with the infiltrant.

[0030] Another alternate process comprises the steps of depositing anindividual freeform part in a vacuum dessicator containing an infiltrantand pressurizing the infiltrant rather than drawing a vacuum. Regardlessof whether a vacuum is drawn on the infiltrant and freeform part, it mayalso be beneficial to heat the infiltrant as pressure is being appliedin order to initiate curing of the infiltrant within the pores of thefreeform part.

[0031] Still another alternate process for modifying the properties of aporous freeform part comprises placing the freeform part in an emptyvacuum dessicator, drawing a vacuum on the freeform part and thenintroducing an infiltrant into the vacuum dessicator such that theinfiltrant enters the pores within the freeform part.

[0032] Although the invention has been described and illustrated withrespect to the exemplary embodiments thereof, it should be understood bythose skilled in the art that the foregoing and various other changes,omissions and additions may be made without departing from the spiritand scope of the invention.

What is claimed is:
 1. A densified freeform-fabricated fiber free partproduced by the process of: (a) providing a porous fiber free freeformfabricated part and depositing said part into a bath comprising aninfiltrant which includes a ceramic precursor or ceramic containingphase; (b) infiltrating the porous freeform fabricated part such thatthe infiltrant enters at least a portion of the pores resulting in adensified freeform fabricated part; and (c) removing the densifiedfreeform fabricated part from the bath.
 2. A densified freeformfabricated part, comprising: (a) a fiber free freeform fabricated parthaving pores therein; and (b) a ceramic or a ceramic containing-phasecontained within a portion of said pores.
 3. The freeform-fabricatedpart of claim 2 wherein the freeform fabricated part is either a metal,ceramic or a mixture thereof.
 4. The freeform fabricated part of claim 2wherein the ceramic or ceramic containing phase originated from aprecursor selected from the group consisting essentially of aluminasol-gel, polysilane, polysilazane, silicon oxycarbide (SiOC),poly(methylvinylsilane), poly(aluminosilazane), perhydridopolysilazane,poly(borosilazane), polycarbosilazane, poly(siloxane), poly(carbosilane)and mixtures thereof.